The present invention relates to reduction of electromagnetic emission, and more specifically to a method for reducing electromagnetic emission, especially in connection with high-performance real-time systems, and for complying with the EMC (ElectroMagnetic Compability) requirements thereof.
From U.S. Pat. No. 5,297,275 (Thayer) there is known a personal computer system comprising variable resolution timers, in which said variable resolution timers are set for the occurrence of the next timer tick interrupt. This arrangement prevents the central processing unit from being loaded unnecessarily with such interrupts, and thereby release processor capacity for other tasks. According to this publication it is also disclosed how the use of dynamic timer ticks can result in the receipt of timer tick interrupts in the central processing unit only at points in time at which this will result in the central processing unit performing a task.
However, from said U.S. publication Pat. No. 5,297,275 there is no reference to using dynamic timer tick interrupts in combination with power-down in order to reduce electromagnetic emission from the CPU in question.
From U.S. Pat. No. 5,481,697 (Mathews et al.) there is known an apparatus for providing a clock signal for a microprocessor at a selectable one of a plurality of frequencies and for dynamically switching between any of said plurality of frequencies. In other words, it is according to this publication suggested to use a variation of the clock frequency in order to adapt the processor speed to what is necessary for performing the task ready to be performed at any time in question. During periods where no task is to be performed there is used a power-down module for further reduction of the power consumption. During these periods this publication suggests timer tick interrupts having a time interval which is specific for the system.
From GB 2 246 455 (Bigwood/Philips) there is known a system in which the rate at which digital circuitry operates, is altered. However, neither this publication nor the previously discussed U.S. Pat. No. 5,431,697 disclose dynamic timer tick interrupts in combination with power-down for reducing electromagnetic emission from the CPU in question.
An object of the present invention is to provide a high-performance real-time system while still complying with EMC requirements.
Another object of the present invention is to provide a method for reducing electromagnetic emission wherein the solution is not handled as a separate hardware issue, thereby avoiding extra cost and possibly extra power consumption.
Still another object of the present invention is to provide a method for reducing electromagnetic emission while at the same time ordering the hardware timer ticks in a more appropriate and versatile manner.
Yet another object of the present invention is to provide a method for reducing electromagnetic emission wherein the CPU in question is awakened only upon applications/tasks requiring full operation of the CPU.
Another object of the present invention is to provide a method for reducing electromagnetic emission in a CPU system wherein only a minimum number of timer ticks are used in between full operation, for example in order to control an expected normal operation of said CPU.
A further object of the present invention is to provide a method for reducing electromagnetic emission in a system while giving improved accuracy of timers, i.e. providing a system wherein the hardware clock and the software timer are more closely tied together to render a higher timer resolution.
Still another object of the present invention is to provide a method for reducing electromagnetic emission in a system wherein the comparator controlling the connection between software and hardware timer ticks, is adapted to megahertz (MHz) clock pulses of the hard-ware clock.
Another object of the present invention is to provide a method for reducing electromagnetic emission in a system wherein the comparator and the software timers are updated according to the expected application or timer handling routine.
Still another object of the present invention is to provide a method for reducing electromagnetic emission, especially in a system wherein high frequency polling is avoided and wherein the protocol-handling is optimized in the most appropriate manner.
The above objects are achieved in a method as stated in the preamble, which according to the present invention is characterized by controlling the access to the CPU bus through CPU powerdown to reduce bus-activity and thereby reduce the electromagnetic emission therefrom.
In an appropriate embodiment this control of the access to the CPU bus may include the reduction of the bus access frequency, thereby reducing the corresponding number of interrupts handled by an interrupt service routine (ISR) and the corresponding number of checks performed by an operation system (OS) scheduler, and consequently increasing the CPU idle time.